Author Topic: A Wallaby of my own.  (Read 252235 times)

Online steamer

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Re: A Wallaby of my own.
« Reply #1005 on: January 16, 2019, 12:24:06 AM »
I’m kinda lost on this crank pin thing. I just can’t see how at this scale and range of rpm running, that hollowing the crank pins would affect balance that much. Now maybe at a several thousand rpm  :shrug:

Cletus

It has an effect.   but it's small compared the difference in materials for the connecting rods.    With the print counterweights, Bronze and weighing 31.4 grams each,  I can run a bronze rod and a Aluminum piston.  My numbers were within a gram of the existing design

The Aluminum rods only needs a 23.4 gram counter weights at the same swing radius.   Now with this engine, I'm wondering if he thought over balance was a good thing

In both the above calculations, I excluded the hollow crank pin.   

Now decisions!    Do I go with the bronze rods?   Go with the cast Z12 alloy rods that I got from Bez? or machine billet aluminum rods?    Hmmmmmm

Dave
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Offline b.lindsey

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Re: A Wallaby of my own.
« Reply #1006 on: January 16, 2019, 12:39:35 AM »
What kind of bearings are used in both ends of the conrods?

Bill

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Re: A Wallaby of my own.
« Reply #1007 on: January 16, 2019, 12:45:37 AM »
What kind of bearings are used in both ends of the conrods?

Bill

Aluminum is aluminum on both ends

Bronze is bronze on both ends

Etc.
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Online steamer

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Re: A Wallaby of my own.
« Reply #1008 on: January 16, 2019, 12:46:44 AM »
Details of the rod
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Offline b.lindsey

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Re: A Wallaby of my own.
« Reply #1009 on: January 16, 2019, 12:48:47 AM »
Ok, so made as part of the rods then as opposed to inserts ( like split bearings). In which care bronze should wear better. Just my opinion though.

Bill

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Re: A Wallaby of my own.
« Reply #1010 on: January 16, 2019, 12:56:37 AM »
Ok, so made as part of the rods then as opposed to inserts ( like split bearings). In which care bronze should wear better. Just my opinion though.

Bill
The Crank case is tight...so I'll probably keep the rods 1 piece.          George runs aluminum rods on his engines....and ETW recommended Aluminum... what with the forced oil lube system, I suspect it will be fine.   As I have ZA12 cast rods to hand.   I think I'll give making those a shot.   ZA12 is about 2/3 the weight of bronze, but with better material properties and excellent bearing properties.   It's a Zinc Aluminum alloy.

Much to consider.....hmmmm
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Online Jo

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Re: A Wallaby of my own.
« Reply #1011 on: January 16, 2019, 07:33:28 AM »
Dave have you noticed that the drawings also shows the option of Ali or Ci pistons. The use of Ali will also cut down on further reciprocating weight.

Jo
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Offline Jasonb

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Re: A Wallaby of my own.
« Reply #1012 on: January 16, 2019, 07:45:27 AM »
If you do use the aluminium option the old "dural" shown on the drawings would equate to 2014, use of other aluminium such as 6061 will not wear well and may well also stretch. It has a small copper content for wear

Online Jo

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Re: A Wallaby of my own.
« Reply #1013 on: January 16, 2019, 08:46:37 AM »
 :headscratch: Where can you buy 6061 in under 50mm diameter round bars ?

Jo
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Offline Jasonb

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Re: A Wallaby of my own.
« Reply #1014 on: January 16, 2019, 09:25:59 AM »
Not many places in the UK as we tend to use 6062 but in the US they use 6061 which is a lot easier to get in our common sizes, Steamer is from the US so I used an example he would know.

First google result https://www.metalsdepot.com/aluminum-products/aluminum-round-bar

2014 for the rods should be available both sides of the pond in small rounds and sections if not 2024 in the US
« Last Edit: January 16, 2019, 10:26:02 AM by Jasonb »

Online steamer

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Re: A Wallaby of my own.
« Reply #1015 on: January 16, 2019, 10:39:13 AM »
Good morning all, and thank you for your interest.

Jason and Jo, Yes   6061-T6 is common here and is what I made the pistons out of.

Any size from 1/4" round on up is readily available here

Conrods....hmmmmm   Still haven't made up my mind on them.   2014 is not readily available here, but 2024-T6 is...as is 7075-T6.

Dave
« Last Edit: January 16, 2019, 10:42:16 AM by steamer »
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Offline Jasonb

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Re: A Wallaby of my own.
« Reply #1016 on: January 16, 2019, 11:34:43 AM »
I see ETW says the crank holes are to aid balancing and that you can make the plugs from Ali

Online steamer

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Re: A Wallaby of my own.
« Reply #1017 on: January 16, 2019, 11:45:37 AM »
Thanks for pointing that out Jason, but the calculations I did last night tend to show that a bronze rod is the overwhelming driver.   Like it didn't even matter.  You need so much counter weight on the crank for the rods, that the crank pin lightening was minuscule.  I'll take another look.

The next real effort is to get the internals complete, including the rods, wrist pins and rings...with the goal of having a rotating assembly by the NEMES show

http://www.neme-s.org/2019_NEMES_show-flyer.pdf.

Dave


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Re: A Wallaby of my own.
« Reply #1018 on: January 17, 2019, 12:28:14 AM »
I'm going to layout a aluminum rod with bronze shell bearings in the big end and a bronze bush in the small end.   Once made and weighed I'll deal with the counterweight, which will be smaller than print size I believe.

7075-T6 for the rods.   Strong and easy to machine.....NEVER going to break...

660 bronze for the bearing shells and bushings.  Known entity.

I'll make the shells first.  They'll drive the rest of it.   0.437 ID   0.500 OD of shell   Flange OD of 0.562.   Width  0.0437 over the flanges, and 0.375 Inside the flanges.   Pinned to the rod to prevent rotation with a bronze pin.    If I can make those shells...we're good to go.   I think I can.

I'll make them the same way I made the main bearing shells ( shown below)  I'll make up 4 full bushings and cut them all in half after I put the pins in.

I'll order the aluminum tonight   I have plenty of bronze.   

Dave
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Offline b.lindsey

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Re: A Wallaby of my own.
« Reply #1019 on: January 17, 2019, 12:35:41 AM »
Should last a long time, won't rust, bust, or collect dust :) Go for it!!

Bill

 

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